[ 3 ] 
certainly no Thermometer fhould be made without ad- 
juftingtwo determinate and fufficiently diftant Points 
of Heat and Cold ; fuch, for inftance, as thofe of 
boiling Water, and of Water juft beginning to freeze, 
and the intervening Space divided into a convenient 
Number of equal Degrees. By this means we fhould 
be able to know what is meant by any fpecified De- 
grees of Heat or Cold, and a Comparifon might 
be eafily made of the State of the Air in diftant 
Places, provided the Inftruments were accurately 
made. 
Dr. Martine feems to think, that the Degree of 
Cold which caufeth Water to begin to freeze, is 
nearly equal in all Places, whatever little Variation 
there may be found in that Degree of Heat which 
caufeth Water to boil, at different times, from the 
different Weight of the Atmofphere: So that we 
may look upon thefe two Points as fufficiently de- 
terminate. 
An Account of an Obfervation I made of the fud- 
den Change of the Temperature of the Air on 
Tuefday the lid of November laft i with the 
State of the Barometer , and other Cirqim- 
ftances . 
On Monday the 21ft in the Evening the Sky very 
clear, the W ind N. and a fmart Froft, the Barome- 
ter was 30 Inches ^ T ™. At near the Thermo- 
meter without my Window at yqr. below o, or 
freezing Point. The Thermometer within, of the 
fame Conftru&ion with it, and not a Yard from it* 
A 2 (the 
